Technical Field
The present disclosure is related to an unlicensed spectrum communication scheme applied in the wireless communication system, and more particular to a method and device for communication on an unlicensed spectrum based on long term evolution (LTE).
Related Art
In the traditional LTE system of 3rd Generation Partner Project (3GPP), the data transmission only occur on the licensed spectrum; however, with the sharp increase in the transmission capacity, especially in some urban areas, the licensed spectrum may be difficult to meet the demand of the transmission capacity. A new research topic is discussed in 3GPP RAN 62 plenary, i.e. the comprehensive research of the unlicensed spectrum (RP-132085), and the main purpose is to research the non-standalone deployment of LTE on the unlicensed spectrum, wherein the so-called non-standalone means that the communication on the unlicensed spectrum is associated with the serving cell on the licensed spectrum. An intuitive approach is to reuse the carrier aggregation (CA) concept in the existing system as much as possible, i.e. the serving cell deployed on the licensed spectrum serves as the primary component carrier (PCC), and the serving cell deployed in the unlicensed spectrum serves as the secondary component carrier (SCC).
In the traditional CA, the user equipment (UE) is capable of being configured with no more than 5 serving cells, and each of the serving cells includes a downlink physical resource and a possible uplink physical resource. For the frequency division duplex (FDD) system, the physical resource is a frequency band, and for the time division duplex (TDD) system, the physical resource is a frequency band and a sub frame. According to the scheduling of the base station, the UE transmits the physical uplink shared channel (PUSCH) data on the uplink physical resource, and receives the hybrid automatic repeat request (HARQ) acknowledgement (HARQ_ACK) to determine whether the PUSCH data is received correctly. The HARQ_ACK is transmitted on the physical HARQ indicator channel (PHICH). The LTE system uses the synchronization PUSCH re-transmission, i.e. if NACK is received, the re-transmission data is transmitted according to the same scheduling initially transmitted, the re-transmission data is transmitted in the predefined sub frame.
For the unlicensed spectrum, considering the non-controllable/predictable of the interference level thereof, the UE may be configured with more uplink carriers, and the base station uses a manner of dynamical frequency selection (DFS) to select a part of uplink carriers for transmitting the PDSCH from the candidate uplink carriers (in a given sub frame). Further, considering the bandwidth of the unlicensed spectrum is larger, for example there is an available unlicensed spectrum of about 500 MHz near the carrier frequency of only 5 GHz, the number of the carriers available for the UE may be quite large (larger than 5).
The traditional carrier aggregation scheme on the unlicensed spectrum communication may encounter the following problems:                the synchronization uplink HARQ limits the application of DFS, i.e. the DFS operation may not performed before the HARQ re-transmission is finished; and        excessive PHICH resources are pre-served, i.e. for each of DFS candidate uplink carriers, it needs preserving a certain PHICH resource, the resources is wasted especially when a quantity of DFS candidate uplink carriers is larger.        
For the above problems, the present disclosure discloses a method and device for the transmission on an unlicensed spectrum.